The present invention relates to a high-voltage pulse generating circuit and a pulse charge-type electrostatic precipitator containing it, and more particularly to a high-voltage pulse generating circuit comprising at least one magnetic pulse compression circuit and an electrostatic precipitator containing such a high-voltage pulse generating circuit.
The pulse charge system is a system in which pulse voltage is generated by the charge-discharge function of a capacitor and added to a de voltage supplied from a de power supply. In an electrostatic precipitator utilizing this system, high-density corona is generated to charge dust efficiently only when pulse is applied. And since corona is not always generated, an average current level can be kept minimum, so that energy consumption is low, and the reduction of reverse voltage can be effectively prevented. As a result, high-electric resistivity dust which cannot be collected by other methods such as an intermittent charging method can be collected by the pulse charge system.
A typical conventional electrostatic precipitator of a pulse charge type is disclosed by Japanese Patent Publication No. 57-43062, Japanese Patent Laid-Open Nos. 59-159671 and 61-185350.
The pulse charge-type electrostatic precipitator disclosed by Japanese Patent Publication No. 57-43062 comprises a high-voltage pulse generating circuit as shown in FIG. 7, which comprises a high-dc voltage generating circuit and an input power supply of the high-voltage pulse generating circuit independently. In FIG. 7, 51 denotes a input power supply of the high-voltage pulse generating circuit; 52 an inductor for charging a main capacitor 53 which serves to store input energy; 54 a switching element for releasing charges stored in the main capacitor 53; 55 a rectifying element for permitting energy to return from a capacitor constituted by dust precipitator electrodes 64 to the main capacitor 53; 56 an inductance element for causing L-C resonance together with a capacitor 59 and a capacitor constituted by the dust precipitator electrodes 64. The capacitor 59 serves to block dc current from flowing from a high-dc voltage generating circuit constituted by the main capacitor 53, a high-voltage dc power supply 62 and an inductor 63 to the high-voltage pulse generating circuit when the switching element 54 is turned on. The inductance element 56 is typically a transformer for increasing pulse voltage applied to the dust precipitator electrodes 64, which comprises a primary winding 57 and a secondary winding 58. Further, in FIG. 7, 60 denotes a negative output terminal of the high-voltage pulse generating circuit connected to a negative input terminal of the dust precipitator electrodes 64, and 61 denotes a positive output terminal of the high-voltage pulse generating circuit connected to a positive input terminal of the dust precipitator electrodes 64. The inductor 63 serves to charge the capacitor constituted by the dust precipitator electrodes 64, and blocks high-voltage pulse generated by the high-voltage pulse generating circuit from flowing into the high-voltage dc power supply 62.
In this electrostatic precipitator containing the high-voltage pulse generating circuit disclosed by Japanese Patent Publication No. 57-43062, energy transferred to the capacitor constituted by the dust precipitator electrodes 64 can be returned to the main capacitor 53, so that energy supplied from the dc power supply to the main capacitor 53 and its consumption can be reduced. As a result, high-resistivity dust can be efficiently collected in practical operations.
However, in the high-voltage pulse generating circuit contained in the pulse charge-type electrostatic precipitator disclosed by Japanese Patent Publication No. 57-43062, it is required for the purpose of reducing energy consumption that a high-voltage pulse output of the high-voltage pulse generating circuit have a smaller pulse width, thereby reducing average output current, and it is also required for the purpose of increasing the service life of the apparatus that the switching element 54 have longer service life and higher reliability.
Accordingly, semiconductor switching elements such as high-speed thyristors, GTO thyristors, etc. are used as the switching element 54, and a plurality of such semiconductor switching elements are used in series to achieve higher breakdown voltage and larger current flow. However, when a plurality of semiconductor switching elements are connected in series to constitute the switching element 54, the pulse width of the high-voltage pulse output of the high-voltage pulse generating circuit can be reduced only to about 30 .mu.s, because each semiconductor switching element constituting the switching element 54 has a critical current increase ratio of at most several hundreds of A/.mu.s or so and a turn-on period of several .mu.s at an absolute maximum rating. Therefore, the average output current of the high-voltage pulse generating circuit cannot sufficiently be reduced, thereby failing to achieve sufficient reduction of energy consumption.
On the other hand, if the pulse width of the high-voltage pulse is further reduced for the purpose of reducing energy consumption, the semiconductor switching elements have insufficient margin with respect to a critical current increase ratio or a turn-on period at an absolute maximum rating, resulting in poor reliability.
Incidentally, the details of the pulse charge-type electrostatic precipitator utilizing the semiconductor switching element are described in "A Pulse Voltage Source For Electrostatic Precipitators," Conf. Rec. of IEEE/IAS Annu. Meet., pp. 23-30, IC (1978).